1. Field of the Invention
The present invention relates to a liquid crystal display (LCD) device, and more particularly, to a viewing-angle image control (VIC) type LCD device that is able to selectively operate in a wide viewing angle mode or a narrow viewing angle mode for both a black-and-white image and a color image, and a method of driving the LCD device.
2. Background of the Related Art
As information technology progresses, flat panel display (FPD) devices having light weight, thin profile and low power consumption have been developed. Among various types of FPD devices, liquid crystal display (LCD) devices have been widely used because of their advantages in resolution, color reproducibility and display quality profile.
In general, an LCD device includes two substrates spaced apart from each other and a liquid crystal layer disposed between the two substrates. There are electrodes formed on the two substrates, to which a voltage is applied to generate an electric field, thereby re-aligning liquid crystal molecules in the liquid crystal layer. Thus, according to re-alignment of the liquid crystal molecules, the LCD device changes light transmittance of the liquid crystal layer to display images.
FIG. 1 is an exploded perspective view schematically showing an LCD device according to the related art. As shown in FIG. 1, the related art LCD device includes a first substrate 10, a second substrate 20 and a liquid crystal layer 30. The first substrate 10, which is referred to as an array substrate, includes a gate line 14 and a data line 16 crossing each other, thereby defining a pixel region P. A pixel electrode 18 and a thin film transistor (TFT) Tr, as a switching element, are positioned in each pixel region P. The TFT Trs, which are each disposed adjacent to the crossing of the gate line 14 and the data line 16, are disposed in a matrix on the first substrate 10. The second substrate 20, which is referred to as a color filter substrate, includes color filter layer 26 including red (R), green (G) and blue (B) color filters 26a, 26b and 26c, a black matrix 25 between the red, green and blue color filters 26a, 26b and 26c, and a common electrode 28 on both the color filter layer 26 and the black matrix 25.
Although not shown in FIG. 1, the first and second substrates 10 and 20 are attached with a seal pattern to prevent leakage of the liquid crystal layer 30. In addition, a first alignment layer is formed between the first substrate 10 and the liquid crystal layer 30 and a second alignment layer is formed between the second substrate 20 and the liquid crystal layer 30, thereby aligning the liquid crystal molecules in the liquid crystal layer 30 along an initial alignment direction. A polarization plate is formed on an outer surface of at least one of the first and second substrates 10 and 20.
Further, a backlight unit (not shown) disposed under the first substrate 10 serves to supply light. A gate signal serves to turn the TFT Tr on and is sequentially applied to each of the gate lines 14, and a data signal on the data line 16 is applied to the pixel electrode 18 in the pixel region P. The liquid crystal molecules in the liquid crystal layer 30 are driven by a vertical electric field generated between the pixel electrode 18 and the common electrode 28 to display images by varying the light transmittance of the liquid crystal layer 30.
Recently, the LCD device has been widely utilized as a display panel for a personal terminal, a portable computer or a mobile phone in a public space. It is occasionally required that the information of the portable device including the LCD device be viewed only by the user and the others around the user should be prevented from watching the information. As a result, a viewing-angle image control (VIC) type LCD device, which is able to selectively display images at one of wide and narrow viewing angles, has been suggested.
FIG. 2 is a plane view schematically showing a VIC type LCD device according to the related art, and FIG. 3 is a cross-sectional view of the VIC type LCD device taken along a line III-III of FIG. 2. As shown in FIGS. 2 and 3, a VIC type LCD device 50 includes first and second substrates 51 and 80 and a liquid crystal layer 90 between the first and second substrates 51 and 80. A gate line 52 and a data line 60 are formed on an inner surface of the first substrate 51. The gate line 52 and the data line 60 cross each other to define first, second, third and fourth pixel regions P1, P2, P3 and P4 constituting a unit region for a color display. A thin film transistor (TFT) Tr is connected to the gate line 52 and the data line 60, and a common line 57 is formed to be parallel to the gate line 52. The TFT Tr includes a gate electrode 54, a gate insulating layer 56, a semiconductor layer 59 including an active layer 59a and an ohmic contact layer 59b, a source electrode 62 and a drain electrode 64.
A plurality of first pixel electrodes 72 are formed in each of the first, second and third pixel regions P1, P2 and P3 and are connected to the drain electrode 64. The plurality of first pixel electrodes 72 each have a bar shape and are spaced apart from each other. In addition, a plurality of first common electrodes 58 are formed in each of the first, second and third pixel regions P1, P2 and P3 and are connected to the common line 57. The plurality of first common electrodes 58 each have a bar shape and alternate with the plurality of first pixel electrodes 72. Further, a second pixel electrode 73 is formed in the fourth pixel region P4. The second pixel electrode 73 has a plate shape and is connected to the drain electrode 64.
A black matrix 82 is formed on an inner surface of the second substrate 80, and a color filter layer 84 is formed on the black matrix 82 and the inner surface of the second substrate 80 in the first, second and third pixel regions P1, P2 and P3. The color filter layer 84 includes red, green and blue color filters 84c, and is not formed in the fourth pixel region P4. An overcoat layer 86 is formed on the color filter layer 84 in the first, second and third pixel regions P1, P2 and P3 and on the inner surface of the second substrate 80 in the fourth pixel region P4. Further, a second common electrode 88 has a plate shape and is formed on the overcoat layer 86 in the fourth pixel region P4.
In each of the first, second and third pixel regions P1, P2 and P3 having the color filter layer 84, a horizontal electric field is generated between the plurality of first pixel electrodes 72 and the plurality of first common electrodes 58 over the first substrate 51, and the liquid crystal layer 90 is controlled by the horizontal electric field, thereby displaying images with a wide viewing angle. In the fourth pixel region P4 having no color filter, a vertical electric field is generated between the second pixel electrode 73 over the first substrate 51 and the second common electrode 88 over the second substrate 80, and the liquid crystal layer 90 is controlled by the vertical electric field to have a relatively high transmittance along an oblique direction with respect to a front direction normal to the second substrate 80 and a relatively low transmittance along the front direction. Accordingly, when a voltage is applied to the second pixel electrode 73 and the second common electrode 88, image display along the oblique direction is restricted by the fourth pixel region P4, and the VIC type LCD device 50 of the related art operates in a narrow viewing angle mode. As a result, the related art VIC type LCD device 50 selectively operates in one of a wide viewing angle mode and a narrow viewing angle mode.
The VIC type LCD device 50 may operates in a narrow viewing angle mode for displaying a black-and-white image such as a document having a text. However, since the fourth pixel region P4 does not include a color filter pattern, the fourth pixel region P4 merely displays a black-and-white image instead of a color image, and does not sufficiently adjust a viewing angle of the VIC type LCD device 50. Accordingly, a color image of the first, second and third pixel regions P1, P2 and P3 is displayed along the oblique direction even when the VIC type LCD device 50 operates in a narrow viewing angle mode.